Composite polymeric material having high resistance to impact energy

ABSTRACT

A method for producing manufactured articles made of composite material comprising the steps of: First completely filling a mold with granules of a pre-expanded polymer in granular form, selected from the group consisting of polystyrene, polypropylene, copolymer of polyphenylene oxide and polystyrene and mixtures thereof; subsequently injecting in the mold an isocyanate mixed with a compound possessing active hydrogen whereby they are filled in void spaces among the granules; and condensing said isocyanate with said compound possessing active hydrogen to yield a polyurethane foam which, by expanding, subsequently completely fills the spaces among the pre-expanded polymer granules.

This is a continuation-in-part application of U.S. application Ser. No.09/100,349, filed on Jun. 19, 1998, now U.S. Pat. No. 6,326,077.

BACKGROUND OF THE INVENTION

The present invention relates to a composite polymeric material havinghigh resistance to impact energy.

Specifically, the present invention relates to a composite polymericmaterial, to the corresponding preparation process and to manufacturedarticles having high impact energy absorption.

Currently, manufactured articles for automotive parts capable ofabsorbing impact energy, such as structures for vehicle interiors andexteriors, motorcycle crash helmets and others, are made of a singlematerial having a polymeric base, such as expanded polystyrene, expandedpolypropylene, or polyurethane foams.

These manufactured articles are generally produced with a moldingtechnology which entails injecting an expandable polymer into a moldhaving a preset shape and then expanding the polymer in the presence ofcatalysts and/or expansion agents. At the end of the expansion, thepolymer hardens and acquires the preset shape of the mold.

In particular, in the production of polyurethane manufactured articles,polyisocyanates and polyesters or glycols are injected into the mold andare made to polymerize in the presence of catalysts and expansionagents. During polymerization, the polyurethane foam forms and, byexpanding, takes the shape of the mold.

However, manufactured articles resistant to impact energy made of asingle polymeric material produced according to conventional technologyare not free from having drawbacks in use, mainly due to the fact thatthey are made of a single polymeric material which does not provide anadequate resistance response to the impact, and to the shock wave. Inparticular, the only variable that is available to the designer is thedensity of the material.

For example, impact-resistant manufactured articles made of a singlepolymer according to the prior art, particularly expanded polystyrenehelmets for motorcycles, have the drawback that they lose theirimpact-resistance characteristics after a single impact that causes apermanent deformation of the structure.

In the case of fenders for cars or of motorcycle helmets, permanentdeformation after an impact accordingly compromises their safetycharacteristics, forcing the user to replace the manufactured article.

SUMMARY OF THE INVENTION

One of the aims of the present invention is to eliminate orsubstantially lessen the drawbacks of the prior art.

Another object of the present invention is to provide a compositepolymeric material which has high-level impact energy resistancecharacteristics and has a long life.

A further object of the present invention is to provide a compositepolymeric material which is simple to produce and does not entail highproduction costs.

Yet another object is to provide a manufactured article made ofcomposite polymeric material which combines low weight with highmechanical strength characteristics.

Another object of the invention is to provide a method for producingmanufactured articles made of an impact-resistant composite materialwhose execution entails modest operating and energy-related costs.

With the foregoing and other objects in view, there is provided, inaccordance with a first aspect of the present invention, a compositematerial comprising a pre-expanded polymer, preferably in granular form,selected from the group consisting of polystyrene, polypropylene, acopolymer of polystyrene with a melting point above 90° C. and mixturesthereof, dispersed in a resin selected from the group consisting ofmelaminic resin, phenolic resin, polyurethane resin and mixturesthereof, the polyurethane resin being the preferred one among them. Theexpression “polystyrene copolymer” denotes a product of polymerizationof polystyrene with another polymer or an alloy of polystyrene withanother polymer.

DESCRIPTION OF PREFERRED EMBODIMENTS

Among polystyrene copolymers having a melting point above 90° C.,preference is given to those with a melting point above 100° C.; amongthese, particular preference is given to the copolymer of polyphenyleneoxide (PPO) and polystyrene (PS). By way of example, mention is made ofthe copolymer of polyphenylene oxide and polystyrene marketed under thetrade-name NORYL EF (in granules or expandable beads) by the GeneralElectric Co., USA, and of the product of the Huntsman Chemical Co.,Chesapeake, Va., USA, marketed under the trade-name GECET (polymericalloy of PS-PPO).

The pre-expanded polymer used in the present invention hasadvantageously been subjected beforehand to an expansion process and hasa granular, spherical or bead-like shape.

The composite polymeric material according to the present inventionpreferably consists of a uniform dispersion of pre-expanded granules orbeads in a matrix of a polyurethane, melaminic or phenolic resin.

Preferably, the polyurethane used in the present invention is obtainedby condensation of an isocyanate or polyisocyanate with a compoundpossessing active hydrogen, both selected so as to have the followingcharacteristics:

low reactivity; a delayed polymerization time of at least about 30seconds allows the two components still in a fluid state to easily reachthe lowest part of a mold wherein pre-expanded granules or beads arepacked and then initiate the polymerization phase, so that when thepolymerisation phase is completed, all (or almost all) the voids amongthe beads are filled with polyurethane (about 50% of the total volume ofthe mold);

optimal cohesion properties and adherence to the expanded beads;

optimal mechanical resistance;

low initial viscosity of the mixture of the two components, allowing aneasy penetration in the voids created among the expanded beads;

high expansion capacity allowing the complete filling of the free spacesso as to obtain a homogeneous structure of the composite material;

high heat resistance;

high self-extinction.

Examples of such components are the isocyanate marketed by Dow ChemicalCo., USA under the name VORACOR CD 526 and the polyol marketed by DowChemical Co., USA, under the name VORACOR CD 443.

The composite material having a polymeric base, according to the presentinvention, has high impact energy absorption because, following animpact, the impact energy is transmitted along the resinous structure,which has acquired a cellular structure whose cells internally containthe expanded polymeric granules, which undergo elastic deformation andconsiderably contribute to damping propagation of the shock wave and toensuring the preservation of impact energy-absorbing properties evenwith subsequent impacts.

In view of these characteristics, the composite material according tothe invention is particularly suitable to provide lightweightmanufactured articles having high mechanical strength and resistance toimpact energy and to repeated impacts.

Said manufactured articles comprise, in variable amounts, the compositematerial according to the invention, alone or associated with otherimpact-resistant materials.

Comparative tests have shown that the manufactured articles according tothe invention have higher energy absorption than polystyrene and, for anequal density with respect to polyurethane, are more resistant to impactenergy and to repeated impacts.

The manufactured articles according to the present invention can beentirely made of the above-described composite material or areconstituted by multilayer structures in which, for example, one or morelayers are made of the composite material and the remaining layers aremade of other materials (polymeric and nonpolymeric).

According to another aspect of the present invention, said manufacturedarticle is a liner for helmets, for example of the type for motorcycles,cars, work or sport. Helmet liners manufactured with the compositepolymeric material according to the invention are highly resistant toimpact energy and in particular maintain their impact-resistancecharacteristics substantially unchanged even after one or more impacts.

In particular, it has been observed that the permanent deformation ofthe surface structure of the manufactured article according to theinvention produced by a medium-energy impact does not compromise, exceptto a limited extent, its strength and safety characteristics, makingthem suitable for prolonged use.

According to a further aspect, the present invention relates to a lifepreserver which comprises the composite material described above.Advantageously, said life preserver is constituted by a core made ofvery hard polymeric material or wood or steel, covered with a layer ofthe composite material according to the invention. The life preserveraccording to the invention has a weight which can be likened to that oflife preservers of the prior art together with high impact resistance.

In accordance with yet another aspect of the present invention, saidmanufactured article is an automotive interior, such as door paddings,door panes, knee bolsters, head restraint systems, sun vizors,instrument panels, rear parcel shelves, or an automotive exterior suchas bumpers, body supports or an automotive cavity filling.

In accordance with another aspect of the present invention, a method forproducing manufactured articles made of composite material is provided,said method comprising the steps of:

injecting into a mold a pre-expanded polymer selected from the groupconsisting of polystyrene, polypropylene, polystyrene copolymer with amelting point above 90° C. and mixtures thereof, and in then injecting aresin or the reagents that polymerize into a resin selected from thegroup consisting of polyurethane resin, phenolic resin, melaminic resinand mixtures thereof;

expanding said resin inside the mold, dispersing said pre-expandedpolymer therein.

Preferably, the pre-expanded polymer is supplied in the form of granulesor beads which have dimensions between 3 and 10 mm and thepolymerization reaction to generate said resin occurs at a temperaturebetween 70 and 140° C.

According to a preferred embodiment of the method according to theinvention, the following operating steps are performed in sequence:

filling a mold with granules of a pre-expanded polymer selected from thegroup consisting of polystyrene, polypropylene, copolymer ofpolyphenylene oxide and polystyrene and mixtures thereof;

subsequently injecting in the mold an isocyanate or a polyisocyanate anda compound possessing active hydrogen thereby they are filled in voidspaces among the granules,

condensing said isocyanate or polyisocyanate with a compound possessingactive hydrogen to generate, by polymerizing, a polyurethane foam which,by expanding, substantially completely fills the spaces among thepre-expanded polymer granules.

It has been observed that by initially filling the mold with thepre-expanded polymer in granular or bead form and then injecting thepolyurethane, it is possible to determine the weight and therefore thedensity of the manufactured article.

Preferably, the reaction for condensation between the isocyanate and thecompound possessing active hydrogen determines a temperature between 70and 140° C. In the execution of the method it is possible to useexpansion agents, additives and catalysts for the condensation reactioncapable of accelerating polymerization and resin hardening times.

The reagents are preferably injected by using positive-displacementpumps with a variable rotation rate and a mixer for mixing the twostreams of reagent.

The term “compound possessing active hydrogen” denotes a compound thatmay be replaced by sodium and with a few compounds having hydrogen atomsnot readily replaced by sodium. In the reaction with said compoundspossessing active hydrogen, the hydrogen atom becomes attached to thenitrogen of the isocyanate and the remainder of the active-hydrogencompound becomes attached to the carbonyl carbon. Said compoundspossessing active hydrogen include compounds having amino, hydroxyl,carboxyl groups, particularly polyesters, polyethers and polyols, thelast being preferred.

The polyurethane condensation or foaming step advantageously entailsexpansion times lasting between 10 and 15 minutes, during which thepolyurethane foam expands into the empty volume between the polymergranules.

In accordance with an embodiment of the method according to theinvention, the mold is filled initially with the pre-expanded polymer.

Preferably, the mold is initially completely filled with beads ofexpanded material with suitable dimensions and bulk density.

The polyurethane resin suitable for use in the present invention has ahigh fluidity and a delayed polymerization time, of at least 30 seconds,so as to allow the passage of the resin through all the expandedmaterial filled in the mold, in the void spaces among the beads.

Moreover, the polyurethane resin used in the present invention has ahigh polymerization heat.

Due to the properties of the isocyanate and active hydrogen containingcompound, as indicated above, in particular due to their high fluidityand low polymerization time, the isocyanate and the active hydrogencontaining compound are filled in substantially all the empty spacesamong the pre-expanded polymer beads.

Due to the granular (or bead-like) shape of the polymer, empty spacesremain between the granules and are gradually filled during theexpansion of the polyurethane resin. A composite material is thusobtained which has a substantially uniform distribution of thepre-expanded polymer granules.

It has been observed that the pre-expanded polymer granules or beads,during the exothermic reaction for the polymerization of thepolyurethane resins, behave differently according to the chemical natureof the polymer being used.

In particular, when granules or beads of expanded polypropylene or of aninterpolymer of polyphenylene oxide and expanded polystyrene are used,the polyurethane condensation reaction can occur at a temperaturebetween 100 and 140° C. without causing their melting or breakdown. Thepolypropylene beads, amalgamated in the polyurethane foam, by beingfilled with air, can compress under the impact energy and then resumetheir initial position, thus dissipating the kinetic energy. It has beenobserved that the resulting composite material has the highestimpact-resistance characteristics.

Instead, when polystyrene granules or beads are used in the process, thegeneration of heat (T=80-100° C.) typical of the exothermicpolymerization reaction of polyurethane causes them to melt. Thegranules, under the heat, melt inside the polyurethane foam, creatingvoids.

The granules or beads used in the process according to the invention areexpandable polymers, expanded for example by subjecting polymericexpandable beads to a pre-expansion in a pressurized vessel using drysaturated steam. Then the pre-expanded beads are subjected to a dryingstep and to a maturing stage to compensate for the temporary vacuum inthe cell structure after pre-expansion. This is achieved, for example,by blowing the prefoam into an air-permeable silo. After sufficient airhas been diffused into the cells, the matured beads are stable and readyfor processing.

The matured prefoam is blown into a mold of the desired shape,preferably until the mold is almost completely filled.

The pre-expanded granules used in the invention preferably have adensity between 10 and 80 g/l, while the resins used preferably have adensity between 20 and 400 g/l.

The method according to the present invention provides manufacturedarticles made of composite material with modest operating andenergy-related costs. In particular, operating costs are reduced thanksto the possibility of using resin molds which are commonly commerciallyavailable at low cost. Molds used in the field of the invention arepreferably thermostat-controlled, so as to maintain a temperature,during the resin polymerization step, that is lower than the meltingtemperature of the foamed polymer described above.

Energy expenditure is reduced due to the low operating temperatures ofthe processing plant.

According to an embodiment of the method according to the invention,manufactured articles of preset shape, such as for example outer shells,reinforcement elements, hooks, nets etcetera, are placed beforehand inthe molds.

The following examples are given merely to illustrate the presentinvention and must not be understood as limiting its scope as defined inthe accompanying claims.

EXAMPLE 1

Three types of helmet were manufactured: each helmet had an outer shellmade of glass fiber and an inner liner having a different composition:

1. Inner liner made of polystyrene with a density of 60 g/l;

2. Inner liner made of polyurethane resin with a density (freeexpansion) of 60 g/l;

3. Innner liner made of the composite material according to theinvention, constituted by an interpolymer of polystyrene and phenylenepolyoxide (GECET) dispersed in polyurethane foam produced bycondensation between polyol (VORACOR CD 443) and isocyanate (VORACOR CD526), both of which are marketed by the Dow Chemical Co., USA.

The three types of helmet were subjected to impact testing according tothe SNELL 95 standard commonly used in helmet testing.

The conditioning temperature was 50° C.

Peak Peak Peak <300 g <300 g <300 g Inc Height Region 1 2 3 HEMI 318 B222 353 209 ″ 235 B 449 500 210 ″ 318 xDx 136 214 195 ″ 233 xDx 242 291198 ″ 318 P 264 219 235 ″ 233 P 300 243 192 ″ 318 R 177 166 195 ″ 233 R324 176 168 ″ 318 xSx 146 245 154 ″ 233 xSx 249 361 213 B,B first andsecond drop test on the front region; xDx, xDx first and second droptest on the right lateral region; P, P first and second drop test on theupper region; R, R first and second drop test on the rear region; xSx,xSx first and second drop test on the left lateral region.

The helmet produced by using the composite material according to theinvention had, following the impact, considerably smaller peaks thanfound when using helmets having a conventional type of inner liner.

Comparative tests show that the material according to the invention isparticularly suitable to form manufactured articles in which high impactresistance is required.

EXAMPLE 2

A method for manufacturing the composite polymeric material according tothe invention.

160 g of expanded beads of Noryl EF (G.E. Co., USA) are injected in aresin mold (volume 8 liters) provided with an air vent Sand shaped likean automotive bumper. An air injector then injects 100 parts by weight(100 g) of VORACOR CD 443 polyol and 110 parts by weight (110 g) ofVORACOR 526 isocyanate.

The polymerization reaction produces a polyurethane foam which expandscompletely in approximately 12 minutes at a temperature of approximately110° C., filling the voids among the foamed polymeric beads.

The mold is then opened and the manufactured article is extracted andfinished according to conventional finishing methods which includecoloring and decorative methods for modifying and peeling the surface.

What is claimed is:
 1. A method for producing manufactured articles madeof composite material, comprising the steps of: first completely fillinga mold with granules of a pre-expanded polymer in granular form,selected from the group consisting of polystyrene, polypropylene,copolymer of polyphenylene oxide and polystyrene and mixtures thereof;subsequently injecting in the mold an isocyanate mixed with a compoundpossessing active hydrogen whereby they are filled in void spaces amongthe granules; condensing said isocyanate with said compound possessingactive hydrogen to yield a polyurethane foam which, by expanding,substantially completely fills the spaces among the pre-expanded polymergranules.
 2. A method according to claim 1, wherein the condensationreaction takes place at a temperature between 70 and 140° C.
 3. A methodaccording to claim 1, wherein said compound possessing active hydrogenis a polyol.
 4. A method according to claim 1, wherein the pre-expandedpolymer is a copolymer of polyphenylene oxide and polystyrene orexpanded polypropylene and in that the polyurethane condensationreaction occurs at a temperature between 100 and 140° C.
 5. A methodaccording to claim 1, wherein the expanded product has a density between10 and 80 g/l.
 6. A method according to claim 1, wherein thepolyurethane resin has a density between 20 and 4000 g/l.
 7. A methodaccording to claim 1, wherein said mold includes a manufactured articlehaving a preset shape.
 8. The method according to claim 1, wherein theisocyanate and the active hydrogen containing compound having apolymerization time higher than 30 seconds.